Multiple-piston pneumatic tool



March 31, l931- F. 1 o. wADswORTH MULTIPLE PISTON PN-EUMATIC TOOL ssheets'fsheet 1 E a mi 3&5 Q E.

Filed Julfy 26, 1921 March 3,1, 1931.

F. L. O. WADSWORTH MULTIPLE PISTON PNEUMATIC TOOL 1921 C5 Sheds-Sheet 2Filed -July 26 /N VEN TOR rA W March 31, 1931- F. L.. o. wADswoRTH1,798,642

MULTIPLE PISTON PNEUMATIC TOOL Filed July 26, 1921 3`Sheets-She'efI 3hNmHli mmm I.mwawwmnh A Patented Mar. 31, 1931 STT Application led July26, 1921.

This linien ion relates to fluid actuated impact mechanisms, such aspneumatic riveting and chipping hammers, compressed air drills ad thelike, which comprise freely movable piston members that are reciprocatedat a high speed to deliver a rapidly recurring succession ,of blowsagainst the heads of relatively stationary toolelements (such as a rivetset or chisel, or a percussion drill); and

one ofthe p imary objects of my present improvement-s is to greatlyincrease the driving, or cutting or penetrating power of such devices,without adding to their weight or bulk.

Under the usual conditions of operationwhere the action of these toolslis dependent only on an impact effect-the maximum capacity of this typeof mechanism is determined, in part by the force of each `blow and inpart bythe number of blows delivered per minute. T ie first factor Vismeasured by the driving energy of the pistonat the instant of its impactwith the operating tool element; and this, in turn, depends on the massor weight of the reciprocating member and on its maximum velocity, orspeed of travel, at that instant of impact. Under a given actuatingpressure on the reciprocating members, which is generally fixed bypractical conditions, the velocity imparted thereto is directlyproportional to the square root of the length oftravel, or the stroke,of the piston, and is inversely proportional to the square root of itsmass. lt lfollows from ,this

that the momentum of each impact blow is directly proportional to thesquare root of the piston stroke and also to the square root of thepiston weight, and that the driving or cutting power of each impulse maytherefore be increased Vby using either a larger piston or a longerpiston cylinder, or both. But the increase in either of these factorsincreases the bulk and weio'ht of lthe mechanism in a much more rapidratio than the individual 5 power impulse is augmented; and the increase'in the effective length of stroke decreases the possible numberofstrokes per minute. rhe aggregate driving power or working capacity ofthese tools, as ordi- 3 narily constructed, cannot therefore ybe `.in-1

Serial No. 487,589.

creased without a great disproportionate enlargement ofthe size, andweight ofthe more important parts of the organization; and this in turnadds not only to the first cost of construction and the subsequentexpense of yoperation and maintenance, but also increases the difcultyand the labor of manipulating these laroer and heavier mechanisms.

in my improved construction I avoid 'all of the dny'ncultieskabovementioned, and ob- 60 tain certain new and important results by.utilizing a. plurality of piston elements to iinpart a properlycontrolled series of blows to a single operating tool. All of therecipron eating members are preferably made of substantially the samesize and weight and are capable of making substantially the same lengthof stroke, which is varied according to an arbitrary rating of capacity(e. g. a ten inch stroke for a No. 10 hammer, atwelve inch 70 stroke fora No. 12 hammer, etc), and the reciprocative movements of the pistonelements are controlled timed, preferably by a single distributionvalve., in such manner that when one of the said elements is making T5its forward or impact stroke, another one is making its rearward orreturn stroke. rlhe number of blows per minute mayV thus be increased toany desired ratio, by increasing the number of co-operatively controlledpis- So tons, without vany decrease either in the .mass or the stroke ofeach reciprocating element,

- andwithout any diminution., therefore, in the driving force of Veachimpulse. A multiple piston tool of my improved construction will, "3 forthis reason, possessa driving power which may be two or three times asgreat asthat possessed .by .the single piston tool of the ordinaryconstruction and of the same rated stroke; and for reasons which willhereafter appear this relatively great increase in the operatingcapacity of the new type of mechanism may be accompanied by an actualdecrease in the bulk and weight of any given size or number (e. g. No.10) of hammer.

Another object of this invention is to improve the operating balance ofreciprocating- ,piston-.impact tools, by the counteracting momentumeffects of voppositely moving piston elements,and thus diminish thetransmis- 100 sion of shock and vibration to the hands of the operators.

A. further object of my improvements is to produce a fluid actuatedimpact tool which does not require the introduction of any change oflive air, o1' live inotivefluid, at the front end of the piston chamber,to effect the rearward or return movement of the reciprocating member,and which does not therefore require, or necessitate, the use of longsupply and exhaust passages extending from the distribution valve to thetool receiving end of the piston cylinder.

Other objects of my present improvements are to produce pneumatic hammerconstructions, which are relatively simple in design and can be readilymanufactured without the use of special tools; which are easilydisassembled and repaired; and which can be operated at low cost.

As illustrative of my invention I have shown, in the accompanyingdrawings, three (3) forms or exemplifications of the multiple pistontype of impact tools; and in the following description of theseexemplifications I have, as far as possible, used the same, or similarreference numerals to denote or designate the same or correspondingparts and elements of the several exemplary organizations.

On the first sheet of drawings, Figure 1 is a longitudinal sectionthrough the center of a twin npiston pneumatic hammer that embodies myimprovements; Fig. 2 is an enlarged cross section on the plane 2 2 ofFig. 1 (or Figs. 3 and 5) Fig. 3 is a fragmentary sectional elevation onthe plane 3 3 of Fig. 2; Fig. 4 is a partial section on this same plane,but showing the distribution valve element in another position; Fig. 5is another fragmentary section on the i plane 5 5 of Fig. 2 (at rightangles tothe plane of the sections shown in Figs. 1, 3 and 4) and Fig. 6is a cross section on the plane 6 6 of Fig. 1.

rlhe second sheet of dra-wings illustrate a second embodiment of myimprovements.

Fig. 7 is a side elevation, partially in section, of this form ofconstruction; Fig. 8 is an enlarged longitudinal section of a partofthe' hammer shown in Fig. 7; Fig. 9 is another 1 similar view of thissame part with the distribution valve element at the opposite end of itsmovement; and Figs. 1l) and 11 are crossscctional views that arerespectively taken on the planes 10-10 and 11 11 of 7.

Figs. 12 to 17, inclusive, depict a third exemplification of myinvention. In these views Fig. 12 is a central longitudinal sectionthrough the rear or handle end of a pneumatic riveting hammer; Fig. 13is a sectional elevation, on the same plane as Fig. 12, of the front orrivet set end of this tool; Fig. 14 is a transverse cross section on theplane 14 14 of Figs. 12-13; Fig. 15 is a longitudinal section on anenlarged scale on the planes 15 15 of Figs. 12-14; Fig. 16 is atransverse section on the plane 1 6 16 of Figs. 12 and 15; and Fig. 17is another view on a still larger scale on this same plane, and showsthe distribution valve elements in another position.

In the construction shown in Figs. 1 to 6 inclusive the hammer barrel 4is provided with two parallel cylindrical chambers, 7 and 8, whichextend from the rivet set collar, or sleeve 9, at the front end of thesaid barrel, to an enlarged cylindrical cavity that receives the valvebox 12 at the rear end thereof. The valve box 12 is provided with twoopenings, which are of the saine diameter as the chambers, 7 and 8, andwhich register therewith, and form extensions thereof when the valve boxis in place. Each of these chambers contains a suitable piston element17, which is adapted to reciprocate freely therein; and which ispreferably provided with a slightly convexed striking face that isadapted to engage with the surface of a curved rib 18 on the inner endof the rivet set shank 19, at such an angle that thek force of the blowsdelivered by the piston elements is directed toward the center of therivet head or other object on which the tool is operating.

The valve box 12 is also provided with two recesses 20 and 21, which aredisposed on opposite sides of the piston cylinder extensions therein;and which are adapted to receive respectively the distribution valveelement 22 and the control valve 23 that regulate the admission of airto the opposite ends of the piston chambers. Live air is admitted to therear ends of these recesses through the lateral passages, 24 and 25`which open into the annular chamber 26 that surrounds the rear end ofthe valve box and communicates at one side with the usual supply duct 27inthe hammer handle. The live air thus admitted to the recess 20 entersthe open end of the hollow distribution valve 22 and passes therefrom,through the ring of ports 28, to one or the other of two annular grooves29 and 30; which are in communication, through the passages 31 and 32,respectively, with two drilled and plugged cavities 33 and 34 (see Fig,3). The cavity 33 is provided with a transverse opening 35, similar inform to that indicated at 41 in Fig. 2, which enters the side of aneccentric groove 36 in the valve box section of the piston chamber 7 andthe cavity 34 is provided with a similar opening 37 that communicates lin like manner with the eccentric groove 38 in the valve box section ofthe other piston chamber 8. The valve box sections of these chambers arefurther provided with two other eccentric grooves 39 and 40, which aresimilar in form to the grooves 36 and 38 and which are positioned at afixed distance in advance of the latter; and these forward channels arein communication with the transverse openings 41 and 42, that enter thedrilled and plugged cavities 43 and 44. rlhe cavity 43 is incommunications through an tothe annular chambers which The space infron1L of the head 6T elongated port l5., with an ecceY tric groove losurroundingl the distribution valve und the cavity lll is incommunication., through a similar port l?, with a revcrselv oilscteccentric groove d8. The recess cont 'ng the trioution valve is alsoprovided wl eccentric groove which communicates through the port withthe exhaust passage 51 that leads to the outside of the hanne barrel (asbest shown in Fig.

The hollow distribulion valve 22 has an cnlarged central portion, whichterminates in the two shoulders 52 and 58 (see l? l), and which carriesa ge /-l that slices in a chamber 55; and this central enlargement isprovided with a peripheral channel 5G whose width is just sutlicient tocover the two adjacent grooves llQ-/lS (when the valve is in theposition of 3 or the t ro adjacent grooves 4G i9 when the valve is inthe position of Fig, l The shell of the valve is perforated by therestricted ducts 57 and which serve to adn it air, from the recess 20,

are respectively located in the rear of the shoulder and in front of theshoulder 53. The e2:- treme rear end of the iirst of these annularchambers is provided with a passageway :E9 which leads forwardly to aport Q in the valve box section of the cylinder and the opposite end ofthe other chamber, in front of the shoulder` 53, is provided with apassageway 61 that leads to a correspondi positioned port 62 in thepiston cylincer 8. The front end of the chamber 55, which the ange lreciprocates, is connected to another port 63, in the front portion thecylinder 7, by means the passageway l; and the rear end of this samechai iber i" connected ito a correspondingly posi@` cned por@ 65 inthecylinc er 8,-by means of the passageway 66.

rlhe control valve which is positionecl line recess 21 comprises plungei 23 and a head 67, that is in cate freely in a two-part t The annularchamber behind the l-.eao 5 connectedL to the live air channel 25, b nof the groove and the duct opening inthe rear o; the sten 231i to theexhaust channel 51, by means of tno ducts 72 and 73 and the peripheralgroove le.

is in 'co-minunication with front part of the recess 21 through the port75; and a passageway T6 leads from the said recess to an opening 7'? inthe partition wall betwee. the cylinders 7 and 8 (see 1). The valveplunger 23-67 is so proportioned that the area of the head portion 67 isabout four times the area of the annular shoulder between kthe said headand the stem and the latter perforated by restricted duct 78, thatserves to connect the ,diferentialarea ,chambers on the two sides of thesaid head, when the valve plunger is in the position shown in Fig. 5.

rllho various bearing surfaces of the reciprocating valve elements and23-67) are ground to form close but easy sliding lits with: theirrespective casings; and the longitudinal movements .of these elementsare limited by the bushing caps or sleeves 8O and 58 that enand coverthe front ends thereof. The assembled valve box parts are clamped inpo-H sition inthe cylindrical recess at the rear end of the hammerbarrel l by screwing on the handleV 1, and locking it in place by meansof suitable ratchet and dog connections 81-82 (such for example as havebeen fully illus--5v trated and described in my co-pending appliationVSerial No. 788,79l, led July 11, 1921) and in order to prevent leakageof liveair from the annula space 26 to the exhaust passages @-51 acompressible wedge-shapedV e xacl-ring ring S3, of aluminum or leadalloy-or similar material, is inserted between the end of the hammerbarrel 4land an internally turned flange on the recessed hub of thehandle member 1. i Sl--SQ and the exhaust openings 51 are covered by aspring ring or clip Se that it provided on one side with dischargeopenings 85 that direct the exhaust away from the handle oortion of thehammer.

The operation of this double piston hammer is as follows:lliencompressed air, or other motive fluid, is admitted to the passage2'? and the annular chamber 26 (by means of the usual thumb valve on thehandle grip),

it will force the controlvalve 23-67 toits forward position, as shown inFig. 5, and permit the motive fluid to flow through the 'passages andports ZS-T-ZG and 77 until the pressure in the front 'end of the pistonff, .-1

chambers, and the space between the two pistons therein, is a littleless than V30% of that inthe annular supply reservoir 26. The pressureon the front face of the valve'head 67 then overbalances the pressure onthe anl r shoulder between this head and the stem 23 and the valve isinovedrearwardly, thus closing the entry end of the-*duct 78 and cuttingoil 'the further flow of motive fluid to the front of the pistonchambers, but leaving that space charged with' air at the reducedpressure just indicated. Yllhe opening of the lsupply passage 27 alsoadmits motive fluid, at the full eservoir pressure, to the interior of lthe 'hollow distribution valve 22; and thence to the rear end ofone ofthe piston chambers 'Z or 8. lfthe distribution valve is in the positionof Fig. 3, the high pressureair flows through .the communicating portsand passages 28-29-31-33-35-36 into the rear end ofthe piston chamber 7'and forces the piston ,therein forwardly. ln this position of the valvethe rear end of the other piston chamber 8 is open to the external airthrough the communicating ports and channels 40- rlhe vlockingconnections D 42-44-47-48-49-50-5l and 85; and the piston in thischamber is therefore driven rearwardly by the low pressure fluid whichias been admitted through the control valve 23-67 and trapped in thespace between the oppositely moving piston elements.

luring the first part of this movement the ports 68 and 65 and passages64 and 66 are open to the low pressure air and the forces acting on thetwo sides of the valve flange 54 are balanced (see Figs. l and ln thispart of the movement the port 60 is open to the high pressure air in therear part of the chamber 7 and the port 62 is open to the exhaust. 'lfhe pressure on the rear of the valve shoulder 52 is therefore greaterthan the pressure on the front face of the shoulder 58, and the valve ismaintained in the position shown in Fig. 8. But when the advancingpiston in the cylinder 7 reaches and passes the port 68 the front faceof the valve flange 54 is exposed to the high pressure air in the rearof the said piston, while the opposite face is still subjected to thelower pressure of the air that is trapped between the reciprocatingmembers. The valve may be so designed that this superior pressure on thefront of the flange 54 will suffice to move the valve rearwardly; but inorder to maintain a more perfect and c ntrolled timing between the twopiston movements l prefer to make the area of the flange 54 considerablyless than the area of the shoulders 52 and 53; and thus delay the throwof the valve until the rearwardly moving piston has reached and coveredthe port 62. lfVhen this occurs the escape of air from the space infront of the shoulder 58 is arrested and the live air flowing into thisspace through the vents 58 immediately raises the pressure thereinsufficiently to move the valve rearwardly to the position shown in Fig.4. This movement placesV the valve openings 28 in communication with thechannel 30 and admits live motive fluid, through the p-orts andpassageways 32-84-37 38, to the rear end of the cylinder 8; andsimultaneously establishes tween the rear end of the cylinder 7 and theexternal air through the ports and passages 39-41`43-45-46-49-50-51-85.The piston in the cylinder 8 is thus driven forward from the dotted lineof position of Fig. l, while the piston in the cylinder 7 is returned bythe pressure of the air that remains trapped between the tworeciprocating elements. The valve 22 is maintained in the position shownin Fig. 4 by the pressure of the live air on the front shoulder 58,until the advancing piston has passed thel port (thus exposing the rearof the flange 54 to the motive fluid pressure back of said advancingpiston) and the rearwardly moving piston has-simultaneously orsubsequentlycovered the port 60 and permitted the live air pressure tobuild up in the rear of the communication be-L shoulder 52 and throw thevalve forwardly, to initiate another cycle of co-operative piston mvements. Each piston is thus caused to move in forced time relationshipwith its mate and to deliver a regularly recurring series of blows onthe rivet set or other operating tool at the forward end of the hammer;and the time ordinarily lost by the return of the piston element to therear of the hammer barrel (in preparation for the succeeding stroke) iscompletely eliminated.

ln the construction shown in Figs. 7 to l1, inclusive7 the two pistonelements 17a and 176 are co-aXially mounted in concentric pistonchambers 7 a and 8a, which are separated from each other by a tube 86,and which are connected at their front ends by the port openings 77a and77 Z). The tube 86 is engaged at its forward extremity by a block 87which is set in the end of the rivet set 19, and which is grooved on itssides to form the equalizing ports 77 b; and it is held at its rear endin a flanged sleeve 88 that is, in turn, clamped between the end wall ofthe hammer handle l and the adjacent recessed end of the valve bonv 12a.The outer surface of the sleeve 88 and the inner concentric surface ofthe valve box, are finished to form the bearing surfaces for thereciprocating distribution valve element 22a; and the enlarged forwardp-ortion of this valve constitutes the rear end of the outer annularpiston chamber 8a. rlhe engaging portions of the tube 86 and the sleeve88 are pierced with a row of ports 81a, which are in radial alignmentwith the ports 28a that pass through the rear endof the valve box andopen directly into the annular reservoir 26 in the hammer handle. rEheinner tube 86 is further perforated with a second row of openings 39athat open into an annular channel 46a between the members 86 and 88; andthis channel in turn communicates with another row of openings 45a inthe outer sleeve 88. The adjacent inner face of the valve box 12a isprovided with a groove or channel 49a which is opposite the openings45a, and which communicates, through the passages 50a and the annularspace 51a, with the radial exhaust ports 51?). The rear portion of thedistribution valve, which reciprocates in the annular space between thesleeve 88 and the concentric bearing surface of the valve casing, isprovided with an end flange 52a (that traverses the ports 28a-31a) andwith an intermediate channeled rib 56a which is pierced with the ports90-90 and which traverses the opposing openings 45a and 49a.

The front part of the valve boX 12a-which receives and guides theenlarged forward portion of the hollow valve 22a-is provided with twogrooves or channels 88a and 40a which communicate respectively with theannularV live air reservoir 26 (through the longitudinal passageways82a) and with the eX- haust openings lmthrough the radial ducts 47a. Thecorresponding portion of the valve shell is perforated with two rows ofmain ports 91 and 92, which are adapted to register respectively withthe channel 38a (when the valve is in the positionshown in Fig. 8) andwith the groove a (when the valve is in the position shown in Fig. 9)and with a third row of auxiliary ports 93, that register with thefirst-named channel when the valve is in its last-mentioned position(Fig. 9). valve bonv is further provided with one or more restrictedducts 57a that lead from the live air reservoir 26 to the annular spacein the rear of the valve flange 52a; and also with similar ducts 78athat lead from the passages 32a to the space behind the front shoulder53a of the distribution element. A longitudinal passage 76a leads fromthe forward end of the annular piston chamber Sa to a point ust back ofthe live air groove 38a; and this passage is provided with two radialducts or ports, 94 and 95, one of which registers with the ports 92(when the valve is in The i the position of Fig. 8) and the other ofwhich opens into the space behind the shoulder 53a and communicates withthe ducts 78a, when the valve has been thrown forward (to the positionshown in Fig. 9). The inner piston chamber 7a is also provided with a.row of ports 96-96 which open into the eXtreme rear end of the annularspace behind the rear valve flange 52a.

The operation of the last described mecha-V nism is as follows: lVhenthe thumb latch of the handle is depressed and live motive fluid isadmitted to the annular reservoir 26, one or the other of the pistonelements will be d l en forward by the flow of the high pres; sure air,either through the ports 3l@ or through the ports 91-and a restrictedamount of wire drawn Huid ill be simultaneously admitted to the front ofthe piston chambers, an d between the two piston elements, through oneor the other of the ports 94 or 95 and the passageway 76a. lf thedistribution valve is in the position shown in Fig. 8, the motive fluidwill enter the rear end of. the cylinder 8a. (through the passages andports 32a* liSd-9i) and drive the annular piston 175 forwardly. ln thisposition the rear end of the central cylinder Ya is open to the externalair through the ports and passages 39e-A6@- Lia 90-50a-5la-5lb-85; andthe piston 17a will therefore be forced rearwardly by the low pressureair that is between it and the advancing piston lia. During the maj orpart of this movement the rear face of the valve flange 59a is notsubjected to any substantial presvbecause the air can escape to the openexhaust, through the ports 96, more rapidly than it can flow in throughthe restricted ducts ct-and the pressure on the front face of theshoulder 53a is considerably greater than the diderential pressure onthe rear face thereof, because of the difference in the areas of thesetwo faces. The valve 22a is therefore held in its retracted positionuntil the rearwardly moving piston laphas covered the ring of ports 39aand thus cut off any further escape of air from the rear end of thecylinder 7a.' The pressure bacl; of the valve flange 52a is then raisedsufhciently to overcome the previously unbalanced pressure on the frontshoulder 53a and the valve is moved forward to the position shown in Fig. 9. This movement closes the ports 91 and opens the ports 31a-thusadmitting live motive fluid to the rear of the piston 17a and drivingthe latter forward-and it also closes the ports a and opens the ports92, thereby permitting the air back of the piston 17?) to escape to theatmosphere, through the passageways 40a-7a-51b-85, and allowing thismember to be` returned by the air that is trapped between the twopistons, and is now maintained at the desired pressure by the slow flowof high pressure fluid through the restricted ducts 'T8Q-95. During themajor period of this reversed action of the piston. valve mechanism thefront face of the valve shoulder 53a is relieved of pressure-by theescape of air through the open exhaust ports 92-and the distributionelement is held in. its advanced position by the full live airv pressureon its rear flange 52a. But when the piston 175 has, in its returnmovement, reached and covered the exhaust ports 92 (as shown in Fig. 9)the fluid in the rear of this member is trapped in the space between itand the valve flange 53a; and the pressure thereon is increased-by thejoint effect of the live air flowing through the restricted ducts 93 andthe compression ofthe trapped fluid by the rearwardly movingpiston-until it is sufficient to overcome the opposing forward pressureson the valve flanges; and the distribution element is then thrown to theposition shown in Fig. 8. This initiates a new cycle of the previouslydescribed movements.

ln the operation of this second exemplifies.- tion Vof my improvedmultiple piston organisation, the maintenance of the desired pressurebetween the'reversely moving pistons is effected by the relatively slowbut continuous iiow of motive fluid into. the passageway either throughthe duct 94, or the ducts 78a and 95-and this flow is so regulated (bya. proper proportioning of the areas of the supply passages) as to justcompensate for any .lealrages,`from the front of the piston chambers,through the rivet set mounting, or

past the rearwardly moving piston to the errhaust. pressure on thereciprocating piston elements is not as sensitive anduniversal in itsaction as the automatic reduction pressure valve 23-67 which isdescribed in connection with the construction shown in Figs. l to 6; butitl This means of controllin the return CIT cure the desired operationof the hammer under very considerable variations in the motive iiuidpressure.

rEhe third illustrative embodiment of my invention, which is depicted inFigs. 12 to 17, inclusive7 presents several features of structure whichare common to both of the previously described mechanismsand which neednot therefore be redescribed in detailbut it presents other features ofconstruction which require additional explanation. For example: The twoorganizations shown in Figs. 1 'to 11, inclusive, are each provided withtwo pistons; whereas the organization now under consideration has fourpistons which operate in pairs in the symmetrically disposed cylinderchambers 76-70, and 86-86. rEhe cylinders T6-7c, and the pistons (170)which work therein, are of somewhat smaller cross-sectional area thanthe cylinders 868c and the corresponding piston elements (17(6) and inorder to make the two pairs of reciprocating members of snbstantiallyequal weight the length of the pistons 170 is somewhat greater than thatof the pistons 176?. The greater length of the firstmentioned membersrequires a greater length of'piston chamber for the maintenance of anequal length of stroke; and this is secured by extending the cylinders'Z6-7c through the valve box 126, (as best shown in Fig. 12) andterminating the cylinders 86-80 at the forward end of that box as shownin Fig. 15)

The distribution valve of this four cylinder construction is made in twoparts 226-220, and is mounted transversely of the valve box between theextensions of the piston chambers 7 6 7 c. These valve parts are mountedin ground and hardened bushings 98 and 99 which are inserted fromopposite sides of the valve box 126, and are held in place, when thevalve box is inserted in the end of the hammer barrel, by the extensionsleeve 100 at the rear end thereof. The rear sides of these bushings 98and 99 are provided with segmental slots 101 and 102 which open into atransverse groove 103 on the back of the valve box 126, and the ends ofthis transverse slot communicate with the live air chamber 26 at thebase of the hammer handle (see Fig. 12). The valve box 126 is furtherprovided with two sets of longitudinal passageways which are arrangedsymmetrically on opposite sides of the valve bushings 98 and 99; andwhich communicate through lateral passageways with two lines of ports inthe side walls of the said bushings. The four longitudinal passageways336 are provided with lateral ports 356 which open into the rear end ofthe piston cylinders 76 and 70; and these passageways communicate,through rows of openings 316 with two annular spaces between the innersurface of the valve bushings 98 and 99 and the intermediate channeledportions 104 and 105 of the distribution valve sections 226 and 220. Thefour longi-l tudinal passageways 346 a-re provided, at their inner endswith transverse ports 376 that open into the rear ends of the cylinders86 and 8c (best shown in Fig. 15) and at their rear ends with transversepassages 326, that also communicate with the annular spaces lastreferred to. The four longitudinal passages 446 are provided, at theirinner ends with transverse ports 426 that also open into the rear end ofthe cylinders 86 and 8c (see Fig. 15), and these passages communicate attheir rear ends with the sides of two peripheral grooves 486 on theexteriors of the bushing elements 98 and 99. The adjacent portions ofthese bushings are perforated with rows of radial ports 476 which serve,in certain positions of the valve elements, to connect the groove 486with the interior of the hollow distribution valve. The ends of thebushings 98 and 99 are cut away on one side to form forwardly extendingslots or channels 106 that register with the rear ends of a series ofexhaust passages 510 in the rear end of the hammer barrel 4. Thedividing web between the four symmetrically disposed piston chambers isfurther provided with a transverse passage 416 that connects therearends of the cylinders 7 6 and 7c; and this transverse passage isconnected with an oval channel 436 that opens, at its rear end, into thecentral portion of the distribution valve recess.

The valve box 126 is also provided with two sets of restricted ducts V576 and 586, which lead respectively from the live air channel 103 to theannular chambers at the outer and inner sides of the valve flanges 526and 536; and the adjacent portions of the valve shells, are perforatedwith rows of small ducts 107 and 108, that are adapted to put the saidannular chambers in communication with the interior of the valve whenthe adjacent flanges are moved away from the contiguous ends of thevalve recesses. The portions of the valve casing in which the reducedends of the valve sections reciprocate are further provided withrestricted ports 596 and 616; and these ports communicate respectivelywith the ports 606 and 626 in the rear ends of the piston cylindersi6-70 and 86-80.

The forward ends of the four piston cylinders are all connected witheach other by an annular opening 109 at the rear of the rivet set sleeve9; and this annular opening is in communication-through thelongitutudinal passageway 766-with a pocket 21 that contains anautomatic control valve 23 which is similar to that illustrated indetail in Fig. 5.

n explaining the operation of this third embodiment of my invention itwill be assumed that the live motive iuid is admitted to the handle whenthe valveparts are in the 1position shown in the enlarged view of Fig.17. rllhe high pressure air will then pass, through the slots 101 and10Q and the passages Slo-SS-Sb, int-o the rear ends of the cylindersfband drive the two pistons therein Jorwardly. In this position the rearends of the cylinders `822- are open to the external air through thecommunicating ports and passageways i26- stelo-'LS-d @-106-510 and 85;and the pistons 17d are therefore ree to move earwardly under the effectof the low pressure air which is admitted to the front end of the pistoncylinders through the passageway 76?) by the previously described actionof the automatic control valve 943-67. Buring this phase of theoperation the pressures on the opposite shoulders 52?) and 53?) of thedistribution valve elements are substantially balanced, because the liveair which is admitted to the annular chambers back of the shoulders 586(through the ducts 58o) is allowed to pass to the exhausted ends of thecylinders 8b and 8c through the now opened ports 612) and 62?); and thelive air that enters the chambers in front of the valve shoulders 52h(through the ducts 57o) is allowed to pass to the exhaust directlythrough the vents 107. But the valve sections are maintained inposition, in part by the frictional resistance to their movement, and inpart by the kinetic pressure edect of the'streams of live motive fluidthat are flowing 'ir-om the slots 101 and 102 inwardly toward tne portopenings 315. But when the rearwardly moving pistons 17d cover theexhaust 1sorts 426 the escape of air from behind the valve flanges 53?)is retarded; and when the continued rearward movement of the pistons hascovered the port 62?) suoli escape is completely arrested; and the rapidresultant building up of the pressure in the now closet chambers back'li the ilanges 536 throws the valve sections 225 and 22o outwardly fromthe position shown in Fig. 1'? to that shown in Figs. 15 and 16.

In this second position of the parts the ports 31o are closed and theports v326 are opened, thus allowing the live motive fluid to flow intothe rear ends'orn tl eA piston chainbers S-Sc and drive the pistonstherein forwardly. The outward movement orn the alve sections also opensthe elongated eX- haust port 482), and allows the air in the rear endsof the piston chambers N2-'Zo to i'low through the interior of thehollow valve sections and pass to the outside of the hammer through thepassageways 10G-510 and 85. ln this phase of the operation the pressureson the end flanges of the distribution valve sections are balanced bythe escape of air Vfrom the annular chamber back of the flange 53?)through the now opened vents 108 and by the escape of air from theannular chamber outside of the flange 52o through the ports 595 and 605;but the valve parts are maintained in position, as betere, by therictional resistance to their movement and by the kinetic pressureeffects of the live air flow through the slots 101 anl 10QJ to the portopenings 32?). When the rearwardly moving pistons 17@ reach and closethe eX- haust openings el?) the -further escape oi air from the chambersin front of the shoulders 525 is retarded; and when these pistons, intheir continued rearward movement reach and cover the ports 605 thatescape is coinpletely stopped. rlhe instantly augmented live airpressure on the outer shoulders of the valve elements then throws theseelements to the iirst described position (illustrated in Fig. 17) andthe various parts are in position to repeat the above-described cycle ofmovements.

in order to obtain the most eifiiciently synized action of the reverselymoving pis- 'n some cases, desirable to so proeleuients 'hat they willhave the l' period Yl3 reciprocation rather lt we ignore theretardiction (which is usually very etiect oic gravity (which may emovement) and assume that essure of the motive fluid on piston remainssubstantially the lull stroke thereof; the

ellective .L the race or tl L '1 constant o.

time, t, oi' each recurrent movement is where m is the mass o thepiston, s is the distance through which it has moved from resti. e., thestroke of the hammer-Agis the area exposed to the motive fluid and p isthe eil-fective pressure. ln the case of cylindrical pistons, the massis equal to the area, A., multiplied 'by the length, Z, and the density,D, oi3 the reciprocating element, and the above eX- pression maytherefore be written ln the particul form of construction illustrated inFigs. 1 to 5, the two piston elements 1 r i and character, and haveln'this case, both equal lengths of strolre ,f s). the masses and tcation of the two elements are the same. But in the constructions shownin Figs. 7 to 11 anl 1Q to 1?', inclusive, one set of piston elenints(17a or lo) is longer than the other t 1'4"?) or 17d) and eachreciprocating member as substantially the saine stroke 3. It the lrainner is to be so designed that each piston rave the saine natural periodof recipro- (25 the product DZ must remain constant; and the meandensity of the longer pistons must therefore be less than that oli' `enatural periods of reciproy the shorter pistons. This result can beattained most conveniently by making the lon er pistons (17a or 170) ofthe form shown in Fig. 1 or Fig. 1n this form the rear end of the pistonis provided with a` cavity 110, which may either be covered by a cap11ithat is pressed and welded in place to form a substantially integralpart of the piston body-or may be left open as shown in Fig. 7.

The hollow or recessed form of piston last described may also beemployed with advantage in certain types of hammer construction in whicheither single or multiple pistons are used. ln percussion impact tools,the useful etico (e) each blow ls determined in part by the kineticenergy of the movingpiston at the time impaetwhich is ieasured by theproduct of the mass times the square of the velocity (o2) of the pistonelement-and in part by the character of the work to be perfori'ned-whiehcontrols the ratio between the kinetic energy of impact and the usefulwork accomplished by the impact actuated member. The aggregate effect(E) of a succession of blows depends upon the individual effect (c) ofeach blow and upon the total number (N) of such blows; and the drivingor cutting power (P) of the tool is, in general, measured by theintegrated effect of these two factors in a fixed interval (or unit) oftime.

Under the conditions assumed in the preceding paragraph, the velocityimparted to a piston of length Z and density D and having i stroke s isV 2fs :JW Dl where f is the force acting, and if we assume that the timeof the return stroke is approximately the same as that of the impactstroke, Ahe number of complete reciprocations (or blows) of a. singlepiston in a given interval of time (T) will be T Z" r Marzi/rit 1f allof the kinetic energy of each blow could be converted into useful workthe e'eet (em) of such blow would be f and the driving power of eachpiston element or for unit of time (T21) wie P 2te/@V Under suchcircumstances, the eEect of each blow (em) would be independent of themass of the piston but would be directly proportional to thecross-sectional area of the reciprocating member and to the length ofits stroke. But the aggregate effect (Em) of a succession of impacts, ona uniformly resistant object, would vary inversely as the square root ofthe mass (m) of the striking member; and in such a case it would,therefore, be an advantage to decrease that mass, without oecreasing thecross-sectional area (il), or the bearing length Z, by the use of theform of hollow piston element that is shown in Figs. 1 and 7.

Under other conditions of operation, the practical efl'eot (e) of eachimpact stroke represents considerably less than the maximum kineticenergy (em) that is imparted to the striking piston; and in many casesthis effect (e) is more nearly proportional to the momentum of pistonmovement (me) than it is to the energy thereof 2 me 2 such cases i ecumulative action of a series of such blows (each of which produces thesame leffeet) is represented by or for unit time (T=1) 1f the charac-terof the work is such that the momentive edect of initial individual blowsis of relatively great importance-as in certain hot riveting or forgingoperaionshit will be of advantage to increase the mass (m) ofthestriking piston; and this can be best accomplished by increasing itsdensity D (in such a manner as is described in my copending applicationSerial No. 488,794 filed July 11, 1921, Jlatent No. 1,739,338 grantedDec. 10, 1929) without increasing its length and thereby diminishing itspossible length of stroke (s). But when the aggregate effect ofrecurrent succession of uniformly acting impulses is to be considered(as in the majority of chipping and drilling` operations) and thecumulative momentive action (E) or effective power (P) is of primaryimportance, the density of the'piston member, and its length of stroke,are immaterial, and the cross-sectional area (A) is the only factor thatrequires consideration. Under such circumstances also, it isadvantageous to employ the hollow or recessed form of piston element(shown in Figs. 1 and 7) because that form is lighter than a solid formhaving the same pressure-receiving area (A) and the same bea-ring length(Z). This last advantage is particularly characteristic of the fourpiston construction shown in Figs. l2 to 17 because in that embodimentof my invention the ratio between the effective pressure area (A) of themoving pistons and the mass thereof 1s increased both by the utilizationof the recessed form of construction for the pistons 17o-170, and alsoby the division of each impact element into two cylindrical members,whose aggregate cross-sectional area 1s considerably greater than thatof a single piston of the normal and usual size and weight.

While I have illustrated and described several embodiments of myinvention, it will be apparent to those skilled in the art that othermodifications, additions and omissions may be made in the apparatusillustrated without departing from the spirit and scope of theinvention, as set forth by the appended claims.

I claim as my invention:

1. In a pneumatic tool, a casing, two piston chambers enclosed withinsaid casing and in open communication at their forward ends, a freepiston located in each chamber, means for delivering motive fluid to thecommunicating ends of said chambers between the pistons, and meansresponsive to variations of pressure within the chambers for controllingthe delivery of motive fluid to and the discharge of motive fluid fromthe rear ends of said chambers.

2. In a pneumatic tool, a casing, two pis- "f ton chambers enclosedthereby, having their forward ends in open communication, a free pistonlocated within each chamber, means responsive to the fluid pressuretrapped in said chambers between said pistons for controlling thedelivery of motive fluid to the communicating ends of said chambers, andmea-ns for controlling the delivery of fluid to and the discharge offluid from the rear ends of said chambers.

3. In a pneumatic tool, a casing, two concentric cylinders locatedtherein, a separate piston operating in each cylinder, a valve boxlocated in the casing and surrounding the rear ends of said cylinders,and a sleeve valve located in said box and surrounding the rear ends ofJthe cylinders for controlling the delivery of operatineV fluid to saidcylinders.

4. In a pneumatic tool, a casing, two concentric cylinders locatedtherein and in communica-tion at their forward ends, a separate pistonoperating in each cylinder, a valve box located within said casing atthe rear of said cylinders and in line therewith, a sleeve valve,located within the box and encircling the rear ends of the cylinders,for controlling the delivery of operating fluid to the rear of saidpistons, and for maintaining a decreased fluid pressure at the forwardends of said cylinders in front of said pis-y tons.

5.l In a pneumatic tool, a casing enclosing two piston chambers in opencommunication at their forward ends, a separate free piston located ineach chamber, a member extending into said casing and engaged by both ofsaid pistons at the forward limit of their strokes, means foralternately delivering high pressure motivel fluid to said chambersbehind said pis-tons and for alternately exhausting said chambers, andmeans for maintaining a reduced operating pressure in the communicatingends of said chambers ahead of said pistons.

6. In a pneumatic tool, a casing enclosing a plurality of pistonchambers in open communication at their forward ends, a separate freepiston in each chamber, a member extending into said casing forming aclosure for the forward end of all of said chambers, and adapted to beengaged by said pistons, a distributing Valve responsive in operation tovariations in fluid pressure within said chambers for delivering highpressure fluid first to one and then another of said chambers and forexhausting one and then another of said chambers and means `formaintaining a reduced fluid pressure in the com municating ends of saidchambers.

7. In a pneumatic hammer, a casing enclosing two piston chambers in opencommunication at their forward ends, a free piston operating in eachchamber, a rivet set extending into said casing and adapted to beengaged by both of said pistons, means responsive to variations inpressure in both chambers for controlling the delivery of fluid to andthe discharge of fluid from the rear ends of said chambers and formaintaining a determined fluid pressure in the communicating ends ofsaid chambers.

8. In a pneumatic tool, a casing enclosing two concentric pistonchambers, in open communication at their forward ends, a memberextending into the forward end of said casing and adapted to be engagedby both pistons, means for controlling the delivery of motive fluid toand the discharge of motive fluid from the rear ends oil said chambers,and means for maintaining a predetermined operating pressure incommunicating ends of said chambers.

In testimony whereof, I have hereunto subscribed my name this 25th dayof July. i 1921.

FRANK L. O. WADSWORTH.

